A model from NOAA's sound-mapping study shows sound fields generated by an average naval sonar training exercise in Hawaii. The red area indicates noise up to 115 decibels, dropping to 40 decibels in the blue.

When a hurricane forced the Nautilus to dive in Jules Verne's "Twenty Thousand Leagues Under the Sea," Captain Nemo took the submarine down to a depth of 25 fathoms, or 150 feet. There, to the amazement of the novel's protagonist, Professor Pierre Aronnax, no whisper of the howling turmoil could be heard.

"What quiet, what silence, what peace!" he exclaimed.

That was 1870.

Today the ocean depths are a noisy place.

The causes are human: the sonar of military exercises, the booms from air guns used in oil and gas exploration, and the whine from fleets of commercial ships that relentlessly crisscross the global seas. Nature has its own undersea noises, but the new ones are loud and ubiquitous.

Marine experts say the rising clamor is particularly dangerous to whales, which depend on their acute hearing to locate food and one another.

To fight the din, the federal government is completing the first phase of what could become one of the world's largest efforts to curb the noise pollution and return the sprawling ecosystem to a quieter state.

The federal effort seeks to document man-made noises in the ocean and transform the results into the world's first large sound maps. The ocean visualizations use bright colors to symbolize the sounds radiating out through the oceanic depths, frequently over distances of hundreds of miles. Several of the larger maps pre­sent the sound data in annual averages — demonstrating how ages in which humans made virtually no contribution to ocean noise gave way to civilization's roar.

Scores of the ocean visualizations have now been made public. The overall purpose is to better understand the cacophony and its impact on sea mammals as a way to build the case for reductions.

"It's a first step," Leila T. Hatch, a marine biologist and one of the project's two directors, said of the sound maps. "No one's ever done it on this scale."

The National Oceanic and Atmospheric Administration began the effort in 2010. Hatch and her colleagues assembled a team of sound experts, including HLS Research, a consulting firm in La Jolla, Calif. Last summer they unveiled their results online, as did a separate team of specialists that sought to map the whereabouts of populations of whales, dolphins and porpoises.

Michael Jasny, a senior policy analyst with the Natural Resources Defense Council, a private group in New York that has sued the Navy to reduce sounds that can harm marine mammals, praised the maps as "magnificent" and their depictions of sound pollution as "incredibly disturbing."

"We've been blind to it," Jasny said. "The maps are enabling scientists, regulators and the public to visualize the problem. Once you see the pictures, the serious risk that ocean noise poses to the very fabric of marine life becomes impossible to ignore."

Legal experts say the new findings are likely to accelerate efforts both domestically and internationally to deal with the complicated problem through laws, regulations, treaties and voluntary noise reductions.

Marine biologists have linked human noises to reductions in mammalian vocalization, which suggests declines in foraging and breeding.

Worse, the Navy estimates that its sonar — used in training and to hunt enemy submarines — results in permanent hearing losses for hundreds of sea mammals every year and temporary losses for thousands. All told, annually the injured animals number more than a quarter-million.

The federal sound study examined all these noises but zeroed in on commercial shipping because it represented a continuous threat, in contrast to sporadic booms. For North Atlantic shipping, the project drew up more than two dozen maps. All their scales went from red (115 decibels at the top) to orange and yellow, and then to green and blue (40 decibels at the bottom). The maps presented the results in terms of annual averages rather than peaks.

Hatch said too many areas of the ocean surface (where sea mammals and whales spend most of their time) are orange in coloration, denoting high average levels.

"It's like downtown Manhattan during the day, only not taking into account the ambulances and the sirens," she said. "I'd be happier saying it was like a national park."

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